This application is based upon European Patent Application No. 97103023.4 filed in the European Patent Office on Feb. 25, 1997, the priority of which is hereby claimed under 35 U.S.C. .sctn. 119. This invention relates to a dental medicine device for pressing a wall molding means against a decayed tooth for restoration thereof, comprising expandable means for urging said wall molding means against the decayed tooth wall to hold restorative material inserted into the tooth.
Dental restoration of cavities between teeth is common practice in dentistry. When it is necessary to restore the portion of a tooth which, prior to decay, contacted an adjacent tooth, it is indispensable to confine the restoration material during placement and until rigid enough, to support itself to conform exactly to the healthy portion of the tooth. Any surplus or overhang of restorative material in the hardly reachable approximal areas constitutes an irritation source which leads to plaque accumulation and constitutes enormous niches for the cariogenic flora. With time, the initially gram-positive flora transforms into parodontopathogenic gram-negative flora which leads to acute and/or chronic periodontal disease.
In order to position the restorative material, it is customary to fit, by means of an appropriate tensioner also called retainer or holder, a matrix band around the tooth for creating a mold to replace the wall lost by caries and cavity preparation during insertion of the restorative material into the tooth. To achieve its function, the matrix band must be fixed in position, and it must be formed as close as possible to the shape of the tooth so that the restorative material placed therein will conform to the outer surface of the healthy portion of the tooth. However, because of the convexity or concavity of the tooth at the site of restoration, the matrix band tends to stand away from the tooth, thereby allowing surplus or overhang of the restoration material to pass between the tooth and the matrix band. This is especially the case when bonding agents and/or flowable composite materials are used to restore the tooth.
Accordingly, a wedging of the matrix band is made, by means of a wedge which is forced between the adjacent teeth in the region between the former contact point and the gingiva to press the matrix band material against the tooth at the floor of the cavity preparation. The wedge is also aiming to perform an additional function in that it forces the teeth apart creating a wider space therebetween than would normally exist. This is important because the matrix band occupies an amount of space which would persist when the matrix band is removed if the elastic memory of the periodental membrane would not move the teeth closer together after removal of the wedge which caused the temporary separation.
Typical wedging technique provides for tapered elongated wooden wedges which may be inserted between adjacent teeth with friction being relied upon to maintain the wedge in position. Since the interdental papilla occupies the approximal space between the teeth, insertion of the wedge causes an injury inducing rubbing compression to the tissue between the teeth. Furthermore, the wedge tends to slip out of position due to the poor frictional engagement provided. As the material forming the wedge is only slightly deformable with practically no elastic memory, all the force applied for placement of the wedge is transmitted to the attachment of the teeth to the bone, with the risk of trauma at this level, whereby the force created by the wedge can be lost. And, most of all, as the tooth contour is quite variable at the site of restoration, with discontinuities and convexities, respectively concavities bordered with convexities, wedge cannot provide more than tangential or point contact between the wedge, the matrix band and the tooth. There is therefore significant pressure on the matrix band area where convexity of the tooth is most pronounced; other areas of the matrix band get only mild pressure or no pressure at all. The result is a loose fit of the matrix band to the tooth, with unavoidable surplus or overhangs of restorative material between the tooth and the matrix band. Of course, it is possible to try to tailor the wedge in an attempt to provide a better fit between wedge, matrix band and tooth; however, this is time consuming and the result is quite aleatory because of difficult to ascertain parameters such as the complex geometry of the tooth and the advance of the wedge between the teeth to assume the required friction fit and pressure of the wedge on the matrix band and tooth.
Where composite resin restorations for light curing technique are used, light transmitting plastic wedges have been developed to transfer light energy for curing of the restorative material. The problems outlined hereabove remain however unsolved, with the added risk that surplus and overhangs of the restorative material may result in leaks in the restorative material which may induce cracks or hollow spaces in the material, thereby reducing its efficiency and creating further niches for the pathogenic flora.
There has been various attempts to provide better wedging. For example, U.S. Pat. No. 3,890,714 shows a plastic wedge with a dihedral body the lateral walls of which are flexible and slotted to increase the friction coefficient between the wedge and adjacent elements; although possibly reducing the risk of trauma at attachment level of the teeth and raising the friction anchor between the teeth, this wedge still cannot solve the problem of a loose matrix band fit; in addition, this wedge has a tendency to lacerate the gingival tissue.
U.S. Pat. No. 3,815,243 discloses a trihedral wedge of soft plastic material with serrations defined by transverse protrusions intended to more evenly distribute the pressure; although outlining the problem of poor matrix band application resulting in surplus of restorative material between the tooth and the matrix band, this wedge still cannot solve that problem because the serrations cannot evenly match the discontinuities, convexities, and concavities of the tooth contour at the site of restoration.
U.S. Pat. No. 4,337,041 refers to a wedge the elongated body of which is provided with depressions intended to positively engage the teeth and simulate the contour of the concave interdental papilla. The wedge is thus preshaped and it can consequently not match the tooth shapes which are different in each case of restoration. The problem of uneven pressure for the matrix band is thus unsolved. In addition, the edges of the depression simulating the contact of the interdental papilla may lacerate the tissue upon insertion of the wedge.
U.S. Pat. No. 5,573,400 describes an expanding dental wedge having a trihedral elongated tapered body. Other cross-sectioned shapes such as trapezoidal or round are possible. This wedge is made of compressed hydrophilic material, such as cellulose or synthetic foams, that expand in contact with moisture. Accordingly, after placement of the matrix band, the wedge is inserted conventionally into the interproximal area between teeth. At this stage, addition of moisture is required to begin an expansion process. The moisture may be applied by the practitioner in the form of water and moisture from the interproximal tissues is said to also enter into matter for the expansion process. The document indicates that the moisture causes a pronounced expansion of the compressed material, providing reciprocal pressure to all points of the matrix band along the proximal surface, thus providing a matrix band seal. The document also indicates that the wedge is more gentle to interdental tissues due to its pliable nature when in contact with moisture. Although this technology may appear appealing, there are serious drawbacks. The expansion and pressure which may result therefrom are totally uncontrollable. The rate of expansion with respect to the amount of moisture is unknown; it is not only bound to the moisture applied by the practitioner, it also depends from variations of the moisture conditions of the gingival tissue and bucal environment, and it further varies as a function of the homogeneity of the compressed material along the length of the wedge. The practitioner has absolutely no means to know how the pressure resulting from the expansion will distribute. The pressure resulting from the expansion may be too low to properly apply the matrix band to sharp convexities or concavities or irregularities of the tooth contour, whereby the risk of poor or loose positioning of the matrix band against the tooth, and the added risk of insufficient force to take the teeth apart from one another. If the pressure is too high than would be required for proper application of the matrix band to the tooth contour there is the added risk of trauma for the teeth attachment. Once the moisture expansion initiated, there is no way to stop or to reduce it otherwise than by a difficult if not impossible drying procedure, whereby the practitioner cannot change the matrix band positioning if he deems it advisable to do so before the restorative material filling procedure. The system therefore cannot be failproof to avoid the risk of surplus or overhangs of restorative material between the tooth and matrix band and the risk of trauma. Apart of this, the document is silent as to how the expanded wedge may be withdrawn from the interdental papilla; forcible withdrawal of the expanded wedge may cause injury to the interdental papilla as well as it may cause an overspacing of the teeth from one another and consequent trauma. Furthermore, rubbing insertion of the compressed dried material may also cause injury to the interdental papilla. And the compressed expandable material forming the wedge does not appear to be appropriate for the transmission of light energy as required for curing plastic or composite restorative materials. Moreover, the wedge is contraproductive since successful handling of filling materials requires 100% dryness. Moisture reduces the quality of restorations. Thus a rubber dam is to be applied to keep the operated area dry.
All references cited herein, including the foregoing, are incorporated herein in their entireties for all purposes.